Air gap autogenesis method

ABSTRACT

A circuit for implementing a registration-free, contiguous conductive plane. A circuit may include a plurality of conductive structures in a first plane. The circuit may further include a contiguous conductive equipotential surface in a second plane parallel to the first plane. The circuit may further include activation means configured to adjust an electric field between the first and second planes thereby activating one or more structures in the fist plane by increasing a potential difference between the first and second planes to a threshold level deemed to constitute an active state. The circuit may further include deactivation means configured to adjust the electric field between the first and second planes thereby deactivating one or more structures in the first plane by decreasing the potential difference between the first and second planes below a threshold level deemed to constitute a deactivated state.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to the following commonly owned copendingU.S. patent applications:

Provisional Application Ser. No. 60/359,783, “Field Sequential ColorPalette Enhancement”, filed Feb. 26, 2002, and claims the benefit of itsearlier filing date under 35 U.S.C. 119(e); and

Provisional Application Ser. No. 60/359,777, “Airgap AutogenesisMechanism”, filed Feb. 26, 2002, and claims the benefit of its earlierfiling date under 35 U.S.C. 119(e); and

Provisional Application Ser. No. 60/359,755, “Extended Gamut FieldSequential Color”, filed Feb. 26, 2002, and claims the benefit of itsearlier filing date under 35 U.S.C. 119(e); and

Provisional Application Ser. No. 60/359,766, “Visible Plus Non-VisibleField Sequential Color”, filed Feb. 26, 2002, and claims the benefit ofits earlier filing date under 35 U.S.C. 119(e); and

Provisional Application Ser. No. 60/359,500, “Common Ground PlaneDischarge Circuit”, filed Feb. 26, 2002, and claims the benefit of itsearlier filing date under 35 U.S.C. 119(e); and

Provisional Application Ser. No. 60/359,501, “Curved Screen FTIR displaymechanism”, filed Feb. 26, 2002, and claims the benefit of its earlierfiling date under 35 U.S.C. 119(e).

TECHNICAL HELD

The present invention relates to the field of flat panel displays, andmore particularly to implementing a registration-free, contiguousconductive plane that is itself flexible and capable of plate bendingmotion either alone or in tandem with an associated elastomeric layer.

BACKGROUND INFORMATION

A flat panel display may comprise a matrix of optical shutters commonlyreferred to as pixels or picture elements as illustrated in FIG. 1. FIG.1 illustrates a flat panel display 100 comprised of a light guidancesubstrate 101 which may further comprise a flat panel matrix of pixels102. It is noted that flat panel display 100 may comprise other elementsthan illustrated such as a light source, an opaque throat, an opaquebacking layer, a reflector, and tubular lamps, as disclosed in U.S. Pat.No. 5,319,491, which is hereby incorporated herein by reference in itsentirety.

Each pixel 102, as illustrated in FIGS. 2A and 2B, may comprise a lightguidance substrate 201, a ground plane 202, a deformable elastomer layer203, and a transparent electrode 204.

Pixel 102 may farther comprise a transparent element shown forconvenience of description as disk 205 (but not limited to a diskshape), disposed on the top surface of electrode 204, and formed ofhigh-refractive index material, preferably the same material ascomprises light guidance substrate 201.

In this particular embodiment, it is necessary that the distance betweenlight guidance substrate 201 and disk 205 be controlled very accurately.In particular, it has been found that in the quiescent state, thedistance between light guidance substrate 201 and disk 205 should beapproximately 1.5 times the wavelength of the guided light, but in anyevent this distance must be maintained greater than one wavelength. Thusthe relative thicknesses of ground plane 202, deformable elastomer layer203, and electrode 204 are adjusted accordingly. In the active state,disk 205 must be pulled by capacitative action, as discussed below, to adistance of less than one wavelength from the top surface of lightguidance substrate 201.

In operation, pixel 102 exploits an evanescent coupling effect, wherebyTIR (Total Internal Reflection) is violated at pixel 102 by modifyingthe geometry of deformable elastomer layer 203 such that, under thecapacitative attraction effect, a concavity 206 results (which can beseen in FIG. 2B). This resulting concavity 206 brings disk 205 withinthe limit of the light guidance substrate's evanescent field (generallyextending outward from the light guidance substrate 201 up to onewavelength in distance). The electromagnetic wave nature of light causesthe light to “jump” the intervening low-refractive-index cladding, i.e.,deformable elastomer layer 203, across to the coupling disk 205 attachedto the electrostatically-actuated dynamic concavity 206, thus defeatingthe guidance condition and TIR. Light ray 207 (shown in FIG. 2A)indicates the quiescent, light guiding state. Light ray 208 (shown inFIG. 2B) indicates the active state wherein light is coupled out oflight guidance substrate 201.

The distance between electrode 204 and ground plane 202 may be extremelysmall, e.g., 1 micrometer, and occupied by deformable layer 203 such asa thin deposition of room temperature vulcanizing silicone. While thevoltage is small, the electric field between the parallel plates of thecapacitor (in effect, electrode 204 and ground plane 202 form a parallelplate capacitor) is high enough to impose a deforming force on thevulcanizing silicone thereby deforming elastomer layer 203 asillustrated in FIG. 2B. By compressing the vulcanizing silicone to anappropriate fraction, light that is guided within guided substrate 201will strike the deformation at an angle of incidence greater than thecritical angle for the refractive indices present and will couple lightout of the substrate 201 through electrode 204 and disk 205.

The electric field between the parallel plates of the capacitor may becontrolled by the charging and discharging of the capacitor whicheffectively causes the attraction between electrode 204 and ground plane202. By charging the capacitor, the strength of the electrostatic forcesbetween the plates increases thereby deforming elastomer layer 203 tocouple light out of the substrate 201 through electrode 204 and disk 205as illustrated in FIG. 2B. By discharging the capacitor, elastomer layer203 returns to its original geometric shape thereby ceasing the couplingof light out of light guidance substrate 201 as illustrated in FIG. 2A.

However, the electrostatic actuators that involve parallel platecapacitor interaction, such as those disclosed in U.S. Pat. No.5,319,491, often involve a large array of variable gap capacitors. Overlarge areas, registration (the term given to the optical alignment andgeometric coincidence of complementary device components topologicallydisposed on either consecutive or nonconsecutive parallel planes inspaced-apart relation) between the discrete top and bottom capacitorplates becomes progressively more difficult to achieve, until theregistration error is multiplied to the point that a large number of topand bottom plates no longer adequately register. That is, the top andbottom plates fail to coincide geometrically due to differentialdimensional drift incurred during fabrication and/or assembly of therespective laminae on which the discrete elements are disposed.Therefore, there is a need in the art to implement a registration-free,contiguous conductive plane that is itself flexible and capable of platebending motion either alone or in tandem with an associated elastomericlayer.

The images displayed on a display, such as the one disclosed in U.S.Pat. No. 5,319,491, do not correspond to physical reality for a numberof reasons, apart from the two-dimensional flattening ofthree-dimensional real world entities. One of the reasons for adisplayed image to not correspond to physical reality involveschrominance. Chrominance is the difference between a color and a chosenreference color of the same luminous intensity. The chrominance range,i.e., the range of difference between a color and a chosen referencecolor of the same luminous intensity, has been limited in order to keepdisplay costs down. Consequently, the gamut of color reproduced on thedisplay is limited. Typically, displays, such as the display disclosedin U.S. Pat. No. 5,319,491, use the three standard tristimulus colors,e.g., red, green and blue (RGB). That is, these displays modulate onlythree primary colors across a screen surface. By increasing the colorsmodulated across the screen surface, i.e., by extending the color gamutdisplayed, the image displayed will more closely correspond to physicalreality. Therefore, there is a need in the art to extend the colorsbeyond the ability of RGB systems to reproduce without extensiblemodifications to such displays.

Furthermore, infrared and other non-visible light displays are generallynot integrated into an existing full color RGB display. There is a needin the art for consolidating RGB and infrared (or other non-visiblelight(s)) in several disciplines, most notably avionics, where cockpitreal estate is at a premium.

Furthermore, the display, such as the one disclosed in U.S. Pat. No.5,319,491, incorporates FTIR (Frustrated Total Internal Reflection)means to emit light from the display surface. If an evanescent wave(such as that produced by total internal reflection), which extendsapproximately one wavelength beyond the surface of a separating mediumof lower refractive index, should be invasively penetrated by a regionoccupied by a higher index of refraction material, energy may flowacross the boundary. This phenomenon is known as evanescent coupling.Evanescent coupling is an effective means to achieve frustrated totalinternal reflection and bears affinity to quantum mechanical tunnelingor barrier penetration.

Flat panel displays, such as the one disclosed in U.S. Pat. No.5,319,491, that incorporate FTIR means are not curved. Consequently, thedistance between the viewer's eyes and the display will vary across thescreen. However, if the display were curved in such a manner that thedistance between the observer's eyes and the screen's equator were equalanywhere along that equator, then the screen would be kept in focus forthe observer. Therefore, there is a need in the art to create such acurved FTIR display screen.

Furthermore, there are various approaches to the problem of efficientlyencoding information displayed on a field sequential color display.These algorithms generally presuppose unmodulated uniformity of the basecolor cycles that are manipulated at the pixel level as performed byU.S. Pat. No. 5,319,491.

FIG. 14 of U.S. Pat. No. 5,319,491 provides a graphic representation ofthe basic technique for generating color. FIG. 14 of U.S. Pat. No.5,319,491 provides a timing diagram relating a shuttering sequence ofthe optical shutter to the 1/180 second strobed light pulses of red,green and blue. It may be appreciated that within any given 1/60 secondcolor cycle various mixes of the three colors may be provided. Thus, asshown in FIG. 14 of U.S. Pat. No. 5,319,491, the first 1/60 second colorcycle provides for a color mix, 3/16 red, 8/16 blue, and 12/16 green.The mixtures obtainable depend only on the cycle rates of the opticalshutter and the color strobing. However, using this method of U.S. Pat.No. 5,319,491 results in a limited palette size. Therefore, there is aneed in the art to increase the available color palette.

Furthermore, there are various approaches to the problem of creatingvoids and complementary standoffs in Microscopic Electro MechanicalSystems (MEMS) structures. Preventing voids in MEMS devices from beingfilled with the next deposition layer is difficult. One method ofattempting to prevent voids in MEMS devices from being filled with thenext deposition layer is to deposit sacrificial layers of specialmaterial in the void. These sacrificial layers of special material areintended to occupy the void until removed by post-processing steps.Hence the term, “sacrificial,” as applied to these special materials.Subsequent layers have the benefit of a flat, non-void surface uponwhich to be deposited. Hence, when the sacrificial layer is removed, thegeometry of the final system is as intended. A void in this context isan empty volume disposed between solid laminae or their equivalents.

Creating standoff structures in the MEMS industry involves complicatedmulti-layer work, where all manners of multiple sub-steps and invocationof so-called “sacrificial” layers is required. Creating “valleys” belowthe level of “plateaus” is a key component in many micromechanicalsystems. Valleys provide mechanical degrees of freedom in which otherelements, which might be ultimately anchored to the plateau, may undergocontrolled motion. These “air gaps” are often the key to many MEMS-baseddevices, but their fabrication remains a complicated process.

MEMS may further require standoffs that are precision registered. Insystems such as the Frustrated Total Internal Reflection Display Systemdisclosed in U.S. Pat. No. 5,319,491, this requirement becomes moreacute in light of the larger area covered by highly detailed MEMSstructures, which become increasingly susceptible to misregistrationeffects during fabrication. Therefore, a simpler fabrication mechanismis called for, preferably one in which sacrificial layers areessentially self-sacrificing without additional fabrication steps beingrequired to generate the standoffs and interstitial air gaps betweenthem.

SUMMARY

The problems outlined above may at least in part be solved in someembodiments of the present invention as addressed below.

The need in the art to implement a registration-free, contiguousconductive plate that is itself flexible and capable of plate bendingmotion may be addressed by the following embodiment of the presentinvention. In one embodiment, a circuit may comprise a plurality ofconductive structures in a first plane. The circuit may further comprisea contiguous conductive equipotential surface in a second plane parallelto the first plane. The circuit may further comprise activation meansconfigured to adjust an electric field between the first and secondplanes thereby activating one or more structures in the first plane byincreasing a potential difference between the first and second planes toa threshold level deemed to constitute an active state. The circuit mayfurther comprise deactivation means configured to adjust the electricfield between the first and second planes thereby deactivating one ormore structures in the first plane by decreasing the potentialdifference between the first and second planes below a threshold leveldeemed to constitute a deactivated state.

The need in the art to extend the colors beyond the ability of RGBsystems to reproduce without extensible modifications to such displaysmay be addressed by the following embodiment of the present invention.In one embodiment, a flat panel display color generating mechanism maycomprise a plurality of individual sources of color light selected tooccupy vertices of a tristimulus color space triangle within a CIE colorspace. The flat panel display color generating mechanism may furthercomprise one or more individual sources of color light selected to lieoutside the tristimulus color space triangle but within the visibleportion of the CIE color space. The flat panel display color generatingmechanism may further comprise an array of pixel structures configuredto modulate light emitted by the plurality of individual sources ofcolor light selected to occupy vertices of the tristimulus color spacetriangle within the CIE color space. The array of pixel structures isfurther configured to modulate light emitted by one or more individualsources of color light selected to lie outside the tristimulus colorspace triangle but within the visible portion of the CIE color space. Afrequency and duration of pulses individually applied to the members ofthe array of pixel structures is selected in response to a number ofcolor light sources outside the tristimulus color space triangle butwithin the CIE color space.

The need in the art to display both RGB images and non-visible imagesfrom a single display may be addressed by the following embodiment ofthe present invention. In one embodiment, a method for producing bothnon-visible and red, green, blue (RGB) images from a single displaysurface may comprise the step of activating RGB lamps configured toproduce RGB images for a first period of time. The method may furthercomprise deactivating a non-visible lamp configured to producenon-visible images for the first period of time. The method may furthercomprise activating the non-visible lamp for a second period of time.The method may further comprise deactivating RGB lamps for the secondperiod of time.

The need in the art to increase the available color palette may beaddressed by the following embodiment of the present invention. In oneembodiment, a method for extending a color palette may comprise the stepof subdividing a primary color into n divisions resulting in n+1intensities for the primary color. The method may further compriseadding m additional subdivisions to the primary color. The method mayfurther comprise activating one or more of a plurality of lamps during afirst m subdivisions of the primary color thereby resulting in theplurality of lamps operating at 1/(m+1) intensity during the first msubdivisions and adding one or more binary bits of information to theprimary color to extend the color palette.

In another embodiment of the present invention, a method for extending acolor palette may comprise the step of subdividing a primary color inton divisions resulting in n+1 intensities for the primary color. Themethod may further comprise adding m additional subdivisions to theprimary color. The method may further comprise adjusting the intensityof a plurality of lamps during a first m subdivisions of the primarycolor resulting in the plurality of lamps operating at 1/(m+1) intensityduring the first m subdivisions and adding one or more binary bits ofinformation to the primary color to extend the color palette.

The need in the art to provide a simpler fabrication of MEMS, preferablyone in which sacrificial layers are essentially self-sacrificing withoutadditional fabrication steps being required to generate the standoffsand interstitial gaps between them may be addressed by the followingembodiment of the present invention. In one embodiment, a pixel maycomprise a substrate layer. The pixel may further comprise an electrodedisposed on an upper surface of the substrate layer. The pixel mayfurther comprise a self-sacrificing layer disposed on an upper surfaceof the electrode. The pixel may further comprise a deformable groundplane disposed on or in close proximity to an upper surface of theself-sacrificing layer. Upon applying a potential between the electrodeand the deformable ground plane, the deformable ground plane may beconfigured to bend towards the electrode thereby crushing theself-sacrificing layer where the crushing of the self-sacrificing layercreates one or more voids.

The foregoing has outlined rather broadly the features and technicaladvantages of one or more embodiments of the present invention in orderthat the detailed description of the invention that follows may bebetter understood. Additional features and advantages of the inventionwill be described hereinafter which form the subject of the claims ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description is considered in conjunction with thefollowing drawings, in which:

FIG. 1 illustrates a perspective view of a flat panel display;

FIG. 2A illustrates a side view of a pixel in a deactivated state;

FIG. 2B illustrates a side view of a pixel in an activated state;

FIG. 3 illustrates an embodiment of the present invention of a circuittopology to implement a registration-free, contiguous conductive plane;

FIG. 4 illustrates an embodiment of the present invention of a side viewof the separation between the deformable ground plane and the pixel padsdisposed on a substrate;

FIG. 5 illustrates a CIE color space depicting both the gamut of normalhuman vision and the gamut of colors displayed by an RGB monitor;

FIG. 6 is a timing diagram depicting the signal pulse widths for fourpixels and the colors blue, green and red used in a display system suchas the display system in U.S. Pat. No. 5,319,491;

FIG. 7 is an embodiment of the present invention of a timing diagramdepicting the signal pulse widths for four pixels and the colors blue,green and red used in a display system incorporating the principles ofthe present invention;

FIG. 8 is a timing diagram depicting the signal pulse widths for fourpixels and the colors blue, green and red in a display system such asthe display system in U.S. Pat. No. 5,319,491;

FIG. 9 is an embodiment of the present invention of a timing diagramdepicting the signal pulse widths for four pixels and the colors blue,green and red as well as infrared output in a display systemincorporating the principles of the present invention;

FIG. 10 illustrates embodiments of the present invention of a displaysystem incorporating FTIR means with a single axis of curvature anddouble axial curvatures;

FIG. 11 is a timing diagram depicting the differences between contiguouspulses and noncontiguous pulses;

FIG. 12 is an embodiment of the present invention of a timing diagramdepicting adding one subdivision to each primary color thereby addingone binary bit to each primary color in a display system incorporatingthe principles of the present invention;

FIG. 13 illustrates an embodiment of the present invention of across-section of a patterned pixel feature;

FIG. 14 illustrates an embodiment of the present invention of crushingan aerogel layer upon applying a potential between an electrode and aground plane;

FIG. 15 illustrates an embodiment of the present invention of restoringthe position of the ground plane to its original position; and

FIG. 16 illustrates an embodiment of the present invention of generatingair gaps and standoff structures being applied to an aerogel substrateone micron thick.

DETAILED DESCRIPTION

The present invention comprises a circuit to implement aregistration-free, contiguous conductive plate that is itself flexibleand capable of plate bending motion. In one embodiment of the presentinvention, a circuit may comprise a plurality of conductive structuresin a first plane. The circuit may further comprise a contiguousconductive equipotential surface in a second plane parallel to the firstplane. The circuit may further comprise activation means configured toadjust an electric field between the first and second planes therebyactivating one or more structures in the first plane by increasing apotential difference between the first and second planes to a thresholdlevel deemed to constitute an active state. The circuit may furthercomprise deactivation means configured to adjust the electric fieldbetween the first and second planes thereby deactivating one or morestructures in the first plane by decreasing the potential differencebetween the first and second planes below a threshold level deemed toconstitute a deactivated state.

In the following description, numerous specific details are set forth toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without such specific details. In other instances,well-known circuits have been shown in block diagram form in order notto obscure the present invention in unnecessary detail. For the mostpart, details considering timing considerations and the like have beenomitted inasmuch as such details are not necessary to obtain a completeunderstanding of the present invention and are within the skills ofpersons of ordinary skill in the relevant art.

Common Ground Discharge Circuit

As stated in the Background Information section, the electrostaticactuators that involve parallel plate capacitor interaction, such asthose disclosed in U.S. Pat. No. 5,319,491, often involve a large arrayof variable gap capacitors. Over large areas, registration between thediscrete top and bottom capacitor plates becomes progressively moredifficult, until registration error is multiplied to the point that alarge number of top and bottom plates no longer adequately register.That is, the top and bottom plates fail to coincide geometrically due todifferential dimensional drift incurred during fabrication and/orassembly of the respective laminae on which the discrete elements aredisposed. Therefore, there is a need in the art to implement aregistration-free, contiguous conductive plane that is, or mayoptionally be, itself flexible and capable of plate bending motioneither alone or in tandem with an associated elastomeric layer.

FIG. 3 illustrates an embodiment of the present invention of a circuittopology 300 to implement a registration-free, contiguous conductiveplane 301 that is itself flexible and capable of plate bending motion.Circuit topology 300 further comprises pixel pad 102 on substrate 101(FIG. 1). Pixel pad 102 may be coupled to an optional stabilizingcapacitor 302 configured to prevent catastrophic collapse duringactuation. As illustrated in FIG. 3, ground plane 301 may be spacedapart from pixel pad 102. Circuit topology 300 farther comprisescircuitry configured to control charging and discharging of thequasi-capacitive structure formed by the conjunction of pixel pad 102and ground plane 301. This circuitry comprises a power source Vcc 303coupled to diode 304 coupled to resistor 306 coupled to ground 307. Thecircuitry further comprises a light emitting diode 305 configured tooptically turn on/off switch 308 coupled to diode 304. In anotherembodiment, ground 307 may be coupled to power source Vdd 308 which maybe coupled to resistor 306. It is noted that although only oneindividual pixel is depicted, it would be understood to one of ordinaryskill in the art that a multiplicity of pixels may be disposed in aspaced apart relation to the common ground plane, such that the gapshave equal initial distance values. It is further noted that a pixel ishere treated as a quasi-capacitive system comprised of two conductiveregions, such as pixel pad 102 and ground plane 301, separated by asimple or complex interstitial dielectric region. In a display screen,these pixels could easily number upwards of one or two million, andsometimes even more. It is further noted that the precise switchingmechanism chosen (exemplified, for example, by components 303, 304, 305,and 306) is representative of a wider range of devices, and that thepresent invention is not limited to the specific choice of exemplar setforth herein to charge and discharge the quasi-capacitive system formedby pixel pad 102 and conductive ground plane 301.

An idealization for the sake of ease of illustration is provided in FIG.4, where sixteen pixels 102 in a 4×4 matrix are disposed in aspaced-apart relation to common conductive ground plane 301. The pixelpads 102 interact, in this illustration, electromechanically with groundplane 301. It is noted that the mode of interactions available forexploitation are not to be conceived as limited to electromechanicalactuation or induced ponderomotive forces. Traditionally, such parallelplate capacitor systems as used in this illustration are composed ofpairs of conductive pads (in the 4×4 example, there would then besixteen lower pads and sixteen upper pads, all of identical size). Inthe present invention, the multiplicity of upper pads may be replacedwith a single contiguous conductive plane 301, thus obviating the needfor careful registration (positioning) of upper pads over lower pads.Further, by replacing the multiplicity of the upper pads with a singlecontiguous conductive plane 301, the need for a complicated trace systemto provide electrical signal flow to each of the upper pads may now beobviated. The trace system (determinative of the geometry of discreteconductive elements and their charge lines) may be limited to the lowerpads, which may be topologically unaffected by implementation of thispresent invention. Alternatively, the single plane 301 could be replacedwith any number of ground planes of a number less than the number ofpixel pads 102 and still be within the scope of the present invention.It is noted that ground plane 301 and the plane upon which pixel pads102 are disposed may be disposed on either Euclidean or non-Euclideansurfaces.

Referring to FIG. 3, the present invention provides the necessarycircuit topology to both charge the quasi-capacitive structure formed bythe conjunction of pixel pad 102 and common ground plane 301,electromotively increasing the potential difference between them (thusdeveloping an attractive force between pixel pad 102 and common groundplane 301 in response to the interstitial electrical field developedduring activation, which leads to a distortion in common ground plane301 in the vicinity centered over the charged pixel pad 102) and todischarge that same quasi-capacitive structure by equalizing thepotential difference between pixel pad 102 and common ground plane 301(reducing the electrostatic attraction to zero, causing the commonground plane 301, which was elastomerically distorted during thecharging cycle, to return to its original geometry). This approach lendsitself well to driving the evanescent embodiment (among others)disclosed in U.S. Pat. No. 5,319,491, (vide FIGS. 16 and 17 therein),but it should be borne in mind that the present invention may begeneralized to systems that do not specifically call for mechanicalmotion or distortion in their several parts. Accordingly, the drivercomponents of FIG. 3 of the present invention (exemplified, for example,by components 303, 304, 305, and 306) that modulate the appliedelectrical signal are representative of an entire class of electricaldrivers, which can be geared to many specific devices, e.g., liquidcrystal display devices. The one micron distance between the pads andplane in FIG. 4 is representative of several mechanical devices, but thepresent invention covers systems where this specific spacing factor isneither critical nor normative, such as in liquid crystal displaysystems.

From an electrical standpoint, the present invention substitutes aconductive equipotential surface for the target layer including aplurality of electrically-active components (referred to as the “upper”elements). Further, the present invention treats charging anddischarging of the remaining “lower” elements (with respect to theconductive equipotential surface) whose complements were concatenatedinto the equipotential surface as a process of switching the systembetween equilibrium and non-equilibrium states as measured between theupper equipotential surface and one or more members of the lowerplurality of discrete elements disposed in spaced-apart relation to theequipotential surface. The terms “upper” and “lower” should be regardedas relative terms useful as heuristic guides, inasmuch as the devicescontemplated generally do not have preferential spatial orientations.

One or more elements or pixels 102 in a conductive plane may beactivated when an electric field between ground plane 301 and theconductive plane is at and/or exceeds a threshold level determined toconstitute an “active state”. One or more elements or pixels 102 in theconductive plane may be deactivated when an electric field betweenground plane 301 and the conductive plane is at and/or below a thresholdlevel determined to constitute a “deactive state”. The activation of oneor more pixels 102 may result in the deformation of ground plane 301, asdiscussed above, as well as ponderomotive action. The deactivation ofone or more pixels 102 may result in a reversal of the deformation ofground plane 301 due to the elastomeric properties of ground plane 301.It is noted that the activated pixels may function in a first state,e.g., on-state, in a binary switch and that the deactivated pixels mayfunction in a second state, e.g., off-state, in a binary switch.

The deformation of ground plane 301 may induce frustrating the totalinternal reflection (TIR) of light in the dielectric substrate uponwhich pixel pads 102 are disposed. Frustrating the TIR of light throughevanescent coupling may be caused by propelling a high refractive indexmaterial in intimate contact with the deformed ground plane 301 into anevanescent field of the dielectric substrate. The evanescent field mayextend upwards of 1 micrometer above the surface of the dielectricsubstrate. The reversal of the deformation of ground plane 301 mayinduce termination of the frustration of the TIR of light.

Referring to FIG. 4, an interstitial dielectric (not shown) may beplaced between ground plane 301 and the dielectric substrate upon whichpixel pads 102 are disposed. The activation of one or more pixels 102may result in changes to the interstitial dielectric (not shown), e.g.,optical, electro-optical, refractive index, optomechanical, opticallynon-linear effects, The deactivation of one or more pixels 102 mayresult in a reversal of the changes to the interstitial dielectric (notshown).

Extending Color Gamut

As stated in the Background Information section, the images displayed ona display, such as the one disclosed in U.S. Pat. No. 5,319,491, do notcorrespond to physical reality for a number of reasons, apart from thetwo-dimensional flattening of three-dimensional real world entities. Oneof the reasons for a displayed image to not correspond to physicalreality involves chrominance. Chrominance is the difference between acolor and a chosen reference color of the same luminous intensity. Thechrominance range, i.e., the range of difference between a color and achosen reference color of the same luminous intensity, has been limitedin order to keep display costs down. Consequently, the gamut of colorreproduced on the display is limited. Typically, displays, such as thedisplay disclosed in U.S. Pat. No. 5,319,491, uses the three standardtristimulus colors, e.g., red, green and blue (RGB). That is, thesedisplays modulate only three primary colors across a screen surface. Byincreasing the colors modulated across the screen surface, i.e., byextending the color gamut displayed, the image displayed will moreclosely correspond to physical reality. Therefore, there is a need inthe art to extend the colors beyond the ability of RGB systems toreproduce without extensible modifications to such displays.

FIG. 5 illustrates a CIE color space depicting both the gamut of normalhuman vision covering the entire CIE diagram and the gamut of colorsdisplayed by an RGB monitor within a triangle commonly referred to asthe “tristimulus triangle”. The primary sources of light in an RGBmonitor, i.e., red, green and blue, occupy vertices of the tristimulustriangle as illustrated in FIG. 5. The colors which can be matched bycombining a given set of these three primary colors, i.e., red, greenand blue, are represented on the chromaticity diagram by the tristimulustriangle joining the coordinates for the three colors. However, thegamut of normal human vision covers colors generated outside thetristimulus triangle. The present invention provides a technique fordisplaying colors outside the tristimulus triangle as discussed below.

FIG. 6 illustrates a timing diagram depicting the signal pulse widthsfor four pixels and the colors blue, green and red used in a displaysystem, such as the display system in U.S. Pat. No. 5,319,491.

FIG. 7 illustrates a timing diagram depicting the signal pulse widthsfor four pixels and the colors blue, green, red, yellow and violet usedin a display system, such as a display system similar to the onedescribed in U.S. Pat. No. 5,319,491, incorporating the principles ofthe present invention as discussed below.

A technique for extending the gamut of colors produced in an RGB systemmay comprise the step of smoothing video without color breakup byensuring that the cycling frequency is sufficiently high. Whenadditional primary colors lying outside the tristimulus color spacetriangle but within the CIE color space are added to the display, thisfundamental requirement may not be relaxed. As illustrated in FIG. 7,two additional primaries lying outside the tristimulus color spacetriangle but within the CIE color space may be added to the RGB systemin order to extend the colors reproduced by the RGB system. It is notedthat any number of additional primary colors, e.g., one additionalprimary color, lying outside the tristimulus color space triangle butwithin the CIE color space may be added to the RGB system and that FIG.7 is illustrative. These pixel structures, e.g., PX1-4 in FIG. 7, areconfigured to modulate light emitted by both the light sources in thetristimulus color space triangle and one or more light sources lyingoutside the tristimulus color space triangle but within the CIE colorspace as illustrated in FIG. 7. The five primary colors, as illustratedin FIG. 7, may have to still fire at the same time that the threeprimary colors had formerly fired, as illustrated in FIG. 6. Theresulting compression is made clear by comparing the source signal pulsewidths between FIGS. 7 and 8. The pixels may also have to be turned onand off more frequently, e.g., at a frequency 67% higher than simple RGBcolor entailed. That is, the frequency and duration of the pulses of thearray of pixel structures, e.g., PX1-4 in FIG. 7, may be selected inresponse to the number of color light sources outside the tristimuluscolor space triangle but within the CIE color space, e.g., 2 additionalprimary colors in FIG. 7.

Selection of additional primaries beyond the tristimulus primaries isdirectly related both to desired color space expansion and imagingacquisition/encoding systems. The present invention may be transparentto these prefatory factors since it exists solely to provide atransducer capable of reproducing the encoded signal (referring toencoding both the tristimulus colors and the colors lying outside thetristimulus color space triangle) on a high pixel density screendisplay.

The color space/color gamut may be enlarged merely by selection of asingle additional primary, but the requisite encoding and image captureequipment may have to be matched to that chosen distal end of the CIEcolor space being stretched beyond the ROB color range. Thus, aquadstimulus color space, as well as a pentastimulus color space, may besupported by the present invention by appropriate modification of theprimary cycles and pixel encodings. Moreover, the present invention mayalso handle color spaces built on more than five colors if this isdesired. Note that there is no explicit requirement that the pulsewidths for each color (in FIG. 7's example, red, green, blue, yellow,and violet) be of identical duration. It is noted that the pulse widthsfor each color in FIG. 7 are shown to be equal in length for ease ofunderstanding. It is not clear whether or not additional primariesbeyond the tristimulus trio of primaries required intensity modulationas tightly controlled as the tristimulus colors need. It is noteworthythat among the tristimulus colors themselves, the human eye shows lesssensitivity to gray scale values in blue than in either red or green. Ifthis fact is true among the base primaries, it may be possible that theanalogy will hold for some or all of the members of the addedcoordinates in the CIE color space provided by the new extended gamutprimaries. In the case of subtractive primaries that have undergonegamut enhancement, the additional fluorescent inks are used sparingly,not heavily. This may be true for colors that spread the display'savailable color gamut as well. Those points in the CIE color space nowrendered available by addition and manipulation of the additionalprimary color light sources might require relatively fewer gray scalesto be effective in providing a smooth, fully-accessible gamut of visiblecolor reproduction.

Adding a desired non-tristimulus vertex to construct an extended-gamutpolygon in the CIE color space may be achieved either by adding one ormore light sources that emit the target color defined at that vertexpoint, or by generating that color by composition of dissimilarsurrogate light sources that chromatically sum up to that vertexlocation based on their weighted intensities. This last strategy mayprove useful given the wide variation in power efficiency that prevailsamong monochromatic light sources currently being manufactured, since adesired primary color that takes considerable power to produce as asingle light source might be achieved with considerably less power ifdistributed between two other colors selected such that the desiredtarget primary lies along the line between these two surrogate lightsources in the CIE color space.

Visible Plus Non-Visible Field Sequential Color

As stated in the Background Information section, infrared and othernon-visible light displays are generally not integrated into an existingfull color RGB display. There is a need in the art for consolidating RGBand infrared (or other non-visible light(s)) in several disciplines,most notably avionics, where cockpit real estate is at a premium.

FIG. 8 illustrates a standard RGB system configured according to thetechnical contours disclosed in U.S. Pat. No. 5,319,491 (vide FIG. 14 inloc. cit), in which four pixels modulate the source lamp intensitiesusing pulse width modulation. It is noted that the technique describedbelow to consolidate RGB and infrared (or other non-visible light) intoa single display may use amplitude modulation as well as pulse widthmodulation. It is further noted that a person of ordinary skill in theart would be capable of applying amplitude modulation using theprinciples of the present invention to consolidate RGB and infrared (orother non-visible light) into a single display. It is further noted thatembodiments applying amplitude modulation using the principles of thepresent invention to consolidate RGB and infrared (or other non-visiblelight) into a single display would fall within the scope of the presentinvention.

In order to produce both RGB color output and gray scale infraredoutput, the device may be reconfigured as illustrated in FIG. 9. Wheninfrared output is desired, as illustrated in the middle bracketedregion of FIG. 9, the RGB primary lamps are shut down and the infraredlamp is activated. This may be referred to as the “infrared mode”. Whenthe RGB primary lamps are activated and the infrared lamp is shut down,this may be referred to as the “RGB mode”. To reactivate the RGB mode,the infrared lamp is deactivated and the successive R-G-B cycle commonto field sequential visible color is reenabled, as illustrated in theright-most bracketed region of FIG. 9. Note that in principle, there isnothing to prevent simultaneous display of visible and infrared imageson the display using field sequential color means, and the informationencoded for these two simultaneously displayed images may be distinctfrom one another. The lamp firing sequence would be a hybridizedsequence such as R-G-B-Infrared in repeated succession, with appropriatesynchronized pixel level modulations applied at the appropriate pointsin this four-part cycle to form the composite image to be displayed.This approach may be extensible to systems that do not have threediscrete primary lamps for red, green, and blue, but rather filter whitelight through color wells or filters in either field sequential oramplitude modulated modes. Pixels operating during the infrared cyclemay either retain their existing ROB encoding, producing a compositegrayscale image in infrared, or a separately optimized infrared signalmay be substituted for the RGB imaging source, as required.

If ultraviolet is substituted for infrared, the screen becomes capableof additional output, although such output is not likely to lend itselfto visual display applications. Microlithography masks may be configuredusing such a system, which may be dynamically programmed and configured.The retention of the RGB profile allows safe inspection of the maskstructure (determined by the pattern of opened pixels) by visual means,to confirm that the topology of the programmed mask encoded in the pixelmatrix matches the actual device. This last concept renders the deviceboth a dynamically programmable photomask that can be continuallyre-used, as well as a display device, suited for verifying and examiningphoto mask circuit topologies without viewing a dangerous ultravioletsignal to do so. This represents a considerable technologicalbreakthrough in the field of printed circuit board and large-scalemicroelectronic systems fabrication, limited only by the pixelresolution of the screen. Displays/dynamic photo mask combinations ascontemplated under this disclosure ought minimally to be able to achievea pixel density of upwards of 1000 pixels per inch.

Curved FTIR Display Screen

As stated in the Background Information section, flat panel displays,such as the one disclosed in U.S. Pat. No. 5,319,491, that incorporateFTIR means are not curved. Consequently, the distance between theviewer's eyes and the display will vary across the screen. However, ifthe display were curved in such a manner that the distance between theobserver's eyes and the screen's equator were equal anywhere along thatequator, then the screen would be kept in focus for the observer.Therefore, there is a need in the art to create such a curved FTIRdisplay screen.

Display Devices, such as the one disclosed in U.S. Pat. No. 5,319,491,involve the injection of light into a substrate that has a higherrefractive index than its immediate surroundings (whether air or acladding of lower refractive index, such as a silica aerogel). Snell'sLaw determines the critical angle at which light entering the substratewill reflect back into the substrate rather than propagate back out atthe point of incidence on the primary planar surfaces. Although theedges of the substrate could likewise constrain light propagation inthis manner—involving constraining the angle of light injection along adimension orthogonal to the constraining angle determined for theprimary planar surfaces—it may be customary to coat the edges withhighly reflective material to create a mirrored inner surface thatpermits greater freedom of light injection angles in the plane parallelto the primary surface. In existing art, the substrates are almostinvariably parallelopiped structures with rigidly rectilinearproportions.

FIG. 10 demonstrates the difference between prior art (inclusive of U.S.Pat. No. 5,319,491, which is a suitable archetype and representative ofthis class of display devices for the purposes of this disclosure) andan embodiment of the present invention, which provides, for single anddouble axis curvatures of the underlying FTIR substrate.

It should be appreciated that the general rules governing the bending offiber optic cables also apply to the present invention. Both fiber opticcables and the present invention exploit the relationships set forth bySnell's Law to preserve the guidance condition whereby light thatinitially propagates by total internal reflection within the interior ofthe guidance substrate continues to do so, notwithstanding the imposedcurvatures, so long as it is not deliberately coupled out of thesubstrate, as would occur at the site of an active pixel disposed at ornear the substrate surface. Where great curvature along a given axis isrequired, optical analysis may possibly dictate additional restrictionof injection angles due to a correlated shift in the value of thecritical angle for total internal reflection to obtain. Excessivecurvature may create a large increase in the noise floor of the displaydevice, rendering it effectively unusable.

FIG. 10 illustrates embodiments of the present invention. In oneembodiment, the present invention may exhibit a single axis of curvature(here arbitrarily shown as lateral). In another embodiment, the presentinvention may exhibit double axial curvatures. Note that introducing acurvature along the third remaining axis would not only distort therectangular shape of the screen, but more importantly would alter therectilinear relationships of the planes intersected by the four edgessuch that orthogonality would no longer apply. Deviation fromorthogonality is not favorably conducive to predictable FTIR operationin most cases, but exceptions exist. Nonetheless, the more importantaxes of curvature exploited in the instant invention are disclosed inFIG. 10.

All FTIR displays that exhibit deviation from Euclidean parallelopipedstructures such that either lateral and/or azimuthal curvature radii arein evidence are claimed for the present invention. The present inventioncovers all relevant applications of such curved FTIR screens, inclusiveof display integration with windshield structures for aircraft andautomobiles, and whether the displays emit only white light, coloredlight (achieved by field sequential color techniques or not), lightbeyond the conventional range defined by the tristimulus colors (red,green, and blue), or nonvisible light (such as infrared or ultraviolet,alone or in any combination with visible lights). For a displayexhibiting both azimuthal and lateral curvature, the principles of thepresent invention may be applied to displays for which the respectivecurvature radii are equal, as well as unequal. The principles of thepresent invention may also be applied to non-Euclidean geometries beyondsimple curves parabolic or higher-order curvatures, negativecurvatures). It is noted that not all of surfaces orthogonal to thelight emitting surface need to constitute actual edges of the dielectriclight guide. It is further noted that those surfaces orthogonal to thelight emitting surface intended for reflection rather than lightinsertion can be structured as virtual planar mirrors created byreflective planes, fabricated by techniques such as reactive ion beametching, that are situated at determinate points interior to thesubstrate and constructed so as to satisfy the orthogonalityrequirement.

Field Sequential Color Palette Enhancement

As stated in the Background Information section, FIG. 14 of U.S. Pat.No. 5,319,491 provides a graphic representation of the basic techniquefor generating color. FIG. 14 of U.S. Pat. No. 5,319,491 provides atiming diagram relating a shuttering sequence of the optical shutter tothe 1/180 second strobed light pulses of red, green and blue. It may beappreciated that within any given 1/60 second color cycle various mixesof the three colors may be provided. It is noted that the presentinvention may function at frequencies both higher and lower than therepresentative values just stated. Thus, as shown in FIG. 14 of U.S.Pat. No. 5,319,491, the first 1/60 second color cycle provides for acolor mix 3/16 red, 8/16 blue, and 12/16 green. The mixtures obtainabledepend only on the cycle rates of the optical shutter and the colorstrobing. However, using this method of U.S. Pat. No. 5,319,491 resultsin a limited palette size. Therefore, there is a need in the art toincrease the available color palette as addressed by the presentinvention discussed below.

The palette size may be increased by using fractional drive lampintensities (whether by amplitude or number of lamps activated) forspecified portions of a subframe cycle. For example, during the firstsubdivision of a primary cycle, the lamps may be set at ½ intensity.This may allow addressing of the subdivision to generate half-integralpixel brightness values, otherwise accessible only by doubling theamount of subdivisions and thus increasing computational bandwidthrequirements in the process. If the first three subdivisions have thelamp intensities set at ¼ of full intensity, this may quadruple thepalette without quadrupling the number of subdivisions. Placing theattenuated drive lamp subdivisions at the leading edge of the cycle maybe required to avoid having more than one on-off signal per pixel percycle while still exploiting common drive lamps for the entire pixelarray. It is noted that the miniscule waste of energy that arises whenthe fractional subdivisions may not be used may be abridged by using tworather than one ½ intensity cycles or four rather than three ¼ intensitycycles. Hence, there is a tradeoff between a tiny energy savings and aslight increase in required bandwidth. The system should track programcontent to determine whether half or quarter integral palette values areneeded, dynamically implementing them on an as-needed basis to conserveenergy.

Field Sequential Color Displays using pulse width modulation techniques(such as the one disclosed in U.S. Pat. No. 5,319,491) create gray scalevalues by dividing a primary color cycle into fractional slices. Thetotal color palette increases as the number of subdivisions increases. Awell-known example is the 24-bit standard where each of the primarycolors (red, green, blue) are divided into 256 subdivisions (2 to theeighth power). The total number of available colors would equal256×256×256=16,771,216 colors. However, the data throughput required toaccess a display screen's pixels 256 times during a primary subcycle(itself typically under 5 milliseconds in duration to ensureflicker-free performance and color-breakup artifacts noted in theliterature) may be impractically high. In the former example, a screenwith one million pixels would have to address all million of them onceevery 21 microseconds, translating to a data throughput requirementexceeding 46 gigabytes per second, with 46 GHz processing power to drivethe encoding process. Pulse width modulation approaches therefore reducethe palette size to manageable proportions, seeking a compromise thatprovides an ergonomically useful palette without placing undue demandson the driver circuitry. Dividing each primary subcycle into 16divisions permits display of a color palette of 4096 colors. The palettesize increases as the cube of the number of divisions.

The present invention may offer a powerful solution to the palette sizeproblem that yields significantly larger palette sizes without acommensurate and impractical rise in real time computing power in thedisplay's driver circuitry. The chief component of this enhancementstrategy involves adjusting the intensity of the drive lamps for certaindeterminate divisions of each primary subcycle. There are two variationsof the present invention, one tailored to contiguous pulse signaldisplays and one tailored to displays capable of noncontiguous pulsesignal processing.

A contiguous pulse signal display is distinctive in that for eachprimary subcycle, there is only one on signal and one off signal. Theentire displayed intensity is released from the display in a singleburst of energy for that primary. A noncontiguous pulse signal displayis capable of being turned on and off more than once during a primarycycle. The total intensity released is the sum of the noncontiguousdurations during which it is active. FIG. 14 illustrates the differencebetween these two approaches to pixel activation.

Referring to FIG. 14, the contiguous pulses may be comparatively simpleto drive since all start times match for any given subcycle, e.g., a redsubcycle, while only one off signal needs to be sent during theremainder of the subcycle. Alternatively, all stop times may match forany given subcycle with one on signal being applied with the resultingintensity equivalent to the former case. The noncontiguous pulsesinvolve sending additional on and off pulses during the subcycle, asillustrated in the right half of FIG. 14.

The palette may be increased under either pixel drive schema with thepresent invention, but the improvement for noncontiguously pulsed pixelsignals may vastly outstrip that of the contiguously pulsed pixel drivesystem. The trade-off is that the electronic overhead to drive pixelsusing noncontiguous pulsing is more severe than that for contiguouspulsing.

In one embodiment, a given pixel drive schema subdivides each primaryinto 7 divisions each for red, green, and blue. With seven divisions,eight possible color intensities may be possible (0 through 7 equals 8total intensities). This may provide a full color palette of 512 colors(8×8×8=512 total combinations of red, green, and blue). Assuming thateach primary color may be driven by four lamps, a total of twelve lampsmay be provided (4 lamps for each primary times 3 primary colors). Underexisting art, palette enhancement would involve increasing thesubdivisions into which each primary subcycle is divided. By increasingthe subdivisions from 7 to 8, the palette may be increased from 512 to729 (9×9×9). This change yields an increase in color palette size ofjust over 42%.

The present invention differs from the current art in providing a 700%improvement in palette size for the preceding example, even though theprimary subdivision is moved from 7 to 8 as before. The criticaldifference lies in the fact that the present invention also controls howmany drive lamps are on at any particular point in the primary subcycle.By having only 2 of the 4 lamps on during the first ⅛of each primarysubcycle, the total palette doubles from 512 to 4096. The first of theeight divisions is configured so that drive lamp intensity is half ofits full value. This is achieved here by adjusting the number of lampsbeing turned on, but the present invention embraces alternate methods toachieve the same result. The most obvious alternative being simpleintensity adjustment of all lamps, or any hybrid combination of thesetwo approaches. In effect, this adjustment adds an additional binary bitof information to each primary. Since there are three primaries, thetotal palette increases by the cube of the added binary bit (two to thethird power equals eight). The before and after comparison is asfollows:

Each primary, original subdivision schema, 7 subdivisions:

0/7, 1/7, 2/7, 3/7, 4/7, 5/7, 6/7, 7/7—total of eight intensities perprimary

Total screen palette=8 cubed=512 colors

Each primary, existing art palette enhancement, 8 subdivisions:

0/8, ⅛, 2/8, ⅜, 4/8, ⅝, 6/8, ⅞, 8/8—total of nine intensities perprimary

Total screen palette=9 cubed=729 colors/42.3% improvement

Each primary, present invention, 8 subdivisions with first subdivisionat ½ lamp intensity:

0/15 through 15/15—total of sixteen intensities per primary

Total screen palette=16 cubed=4096 colors/700% improvement

Note that the overall maximum screen output will drop slightly when thepresent invention is implemented to increase palette size, since thelamp intensity is halved for one eighth of each subcycle. In the aboveexample, this may result in a drop in maximum intensity of 6.25%.Although maximum intensity may have dropped, there may be no change inefficiency, since energy consumption may have dropped by the sameamount. Accordingly, this drop may be compensated simply by increasingthe energy to the drive lamps by the corresponding factor to offset theintensity drop, with no change in system efficiency.

For contiguously pulsed pixels, additional palette enhancement may beachieved by extending the preceding principles as follows:

(1) To add one binary bit of information, add one subdivision (as inexample above), yielding an overall improvement in palette size of 700%(2 cubed) when the lamps are at half intensity during the firstsubdivision. Total palette size: 4096 colors. Existing art provides 729colors (9 cubed).

(2) To add two binary bits of information, add three subdivisions toyield an overall improvement in palette size of 6300% (4 cubed) when thelamps are at quarter intensity during the first three subdivisions.Total palette size: 32,768 colors. Existing art provides 1331 colors (11cubed).

(3) To add three binary bits of information, add seven subdivisions toyield an overall improvement in palette size of 51,200% (8 cubed) whenthe lamps are at one-eighth intensity during the first sevensubdivisions. Total palette size: 262,144 colors. Existing art provides2744 colors (14 cubed).

By controlling drive lamp) intensity and encoding the leading edge ofpixel activations to utilize none, part, or all of these fractionallamps intensities, tremendous advances in palette size may be achievedwithout the commensurate increase in computing power needed to drivecurrently required in the existing art. Further, there may be areduction in maximum optical output when the present invention isimplemented. Further, since it does not affect efficiency, powercompensation to the drive lamps to readjust maximum intensity may notharm device efficiency. The reduction in maximum optical output may varyfor each of the above representative scenarios. For example, thereduction in maximum optical output may be 6.25% for case (1) above,22.5% for case (2) above, and 39.4% for case (3) above. Globallyadjusting lamp intensity by these factors will yield the originalmaximum display intensity without changing energy efficiency. Thecompensation essentially corrects for the fact that the lamps do notemit at full intensity during the succession of primary subcycles. Asbefore, the reduction of lamp output may be achieved either by alteringthe quantity of lamps being turned on, or by adjusting input energy tothem to reduce their output during the subdivisions during whichfractional intensity may be required, or a combination of these twotechniques.

Where the intensity of the lamps is controlled by manipulating thenumber of lamps lit, the present invention also prescribes rotating theoff-duty lamps so that overall duty cycle is balanced between all thelamps. For example, in a four lamp per primary system under scenario (1)above, only two of the four lamps are on during the first subdivision.The lamps to remain inactive during these fractional intensitysubdivisions should be rotated to balance out their duty cycles, e.g., 1& 2, then 2 & 4.

Generally, a balance between full intensity subdivisions and fractionalintensity subdivisions should be sought. The trade-off is easy todiscern. If too many fractional subdivisions are used, the lamps may berequired to be driven to high output levels to compensate for thereduction in maximum optical output. While this may be reasonable forall illumination technologies for scenarios (1) through (3) above, thismay not be likely to be the case for certain illumination systems.

An illustration of how the present invention's addition of oneadditional binary bit to each primary is achieved in relation to pixeloperation is illustrated in FIG. 15. Referring to FIG. 15, the intensitynotch at the leading edge of each lamp on-cycle for each pixel mayrepresent the appropriate encoding of gray scale information to takeadvantage of the half intensity lamp subdivision. The relative area ofthe notch may constitute the intensity loss in the system. Since theenergy consumption tracks with that intensity, overall efficiency is, asbefore, unaffected by implementation of the present invention.

For contiguously pulsed pixel systems previously considered, newsubdivisions may be added to each primary according to the formula2^(n)−1, for n=1, 2, or 3 additional binary bits per primary in theexamples provided. It is noted that n is not limited to these values andthese values are illustrative. For the three examples previouslydiscussed, this amounted to adding, respectively, one ½ intensitysubdivision, or three ¼ intensity subdivisions, or seven ⅛ intensitysubdivisions. Since the pixel pulses are contiguous (only one pixel-onand pixel-off signal per primary subcycle), the formula holds.

If the pixels can be pulsed noncontiguously, however, there are superiorways for achieving increases in the binary bit depth of the primary grayscales. There may be no actual difference for achieving an improvementof only one binary bit per primary, since by definition the ½ intensitysubdivision, being only one in number, is in fact contiguous to the fullintensity lamp pulse that follows it. However, for the 2-bit and 3-bitper primary palette enlargement schemas, the improvement clearlyfollows. To provide a 2-bit per primary improvement in a noncontiguouslypulsed display, two subdivisions may be added (rather than three as inthe contiguous case), but the lamp intensities for these two divisionsare ¼ and ½ intensity, respectively. In the 3-bit per primaryenhancement, three subdivisions (rather than seven) may be added, butthe lamp intensities for these three divisions are ⅛, ¼, and ½intensity, respectively. As before, lamp intensity may be subdividedeither by controlling how many lamps are on, or by modulating the energyprovided to illuminate them, or a combination of these two techniques.

The importance of noncontiguous pulsing of pixels becomes clear,particularly in the case last described. The first three subdivisions,during which the lamps are at ⅛, ¼, and ½ intensity, may be combined indifferent combinations to achieve any value of the form n/8, where n<8.However, only half of the combinations (0, ½, ¾, and ⅞) may be achievedwith contiguous pulsing. The other values (⅛, ¼, ⅜ and ⅝) requirenoncontiguous pulsing in order to prevent the pixel from being on duringundesired subdivisions. In this example, pixel activation/deactivationmay occur up to twice per primary subcycle in order to produce allavailable colors in the enhanced palette. If the palette is expanded byadding an additional subdivision at 1/16 intensity (4 total additionalbinary bits per primary color), additional on-off cycles per primarysubdivision may be required in order to generate all sixteen fractionalvalues during the first four subdivisions.

As in the contiguous pulsed case, real time conversion of incoming grayscale values to the appropriate pixel activation sequence during eachprimary color subcycle may be configured to take advantage of thepresent invention herein disclosed. It is significant that noncontiguouspulsing expands the color palette with a lower impact on maximum screenintensity, thus requiring less compensation at the drive lamp inputside. As before, overall efficiency may not be affected by eithervariant of the present invention.

Both variants demonstrate vastly superior palette enhancement over theexisting art for all sequential color displays that use any form ofpulse modulation. It is noted that the technique may be applied toamplitude modulated field sequential color if temporal control of pixelamplitude may be synchronized to fractional backlight intensitiesanalogous to those illustrated in FIG. 12.

Technique to Create Air Gaps and Standoff Structures Without ElaborateInterlayer Registration

As stated in the Background Information section, creating stand-offstructures in the MEMS industry involves complicated multi-layer work,where all manner of multiple sub-steps and invocation of so-called“sacrificial” layers is required. Creating “valleys” below die level of“plateaus” is a key component in many micromechanical systems. Valleysprovide mechanical degrees of freedom in which other elements, whichmight be ultimately anchored to the plateau, may undergo controlledmotion. These “air gaps” are often the key to many MEMS-based devices,but their fabrication remains a complicated process.

MEMS may further require standoffs that are precision registered. Insystems such as the Frustrated Total Internal Reflection Display Systemdisclosed in U.S. Pat. No. 5,319,491, this requirement becomes moreacute in light of the larger area covered by highly detailed MEMSstructures, which become increasingly susceptible to misregistrationeffects during fabrication. Therefore, a simpler fabrication mechanismis called for, preferably one in which sacrificial layers areessentially self-sacrificing without additional fabrication steps beingrequired to generate the standoffs and interstitial air gaps betweenthem as addressed by the present invention discussed below.

FIG. 13 illustrates an embodiment of the present invention of across-section of a patterned pixel feature 1300. Patterned pixel feature1300 may comprise a substrate 1301 formed of various well known lightguiding materials, e.g., Lucite, of high refractive index. Disposed onthe upper surface of substrate 1301 may be a patterned electrode 1302.Disposed on the upper surface of patterned electrode 1302 may be anaerogel 1303. In one embodiment, aerogel 1303 may be atetramethoxysilane aerogel that is between 0.8 μm and 1.1 μm inthickness. Disposed on the upper layer of aerogel 1303 may be acontiguous ground plane 1304 such as ground plane 301 (FIGS. 3 and 4).Accordingly, the electrical gap is small enough to allow considerablemechanical force to be developed using electrostatic means withoutexceeding the dielectric strength of aerogel 1303. Upon applying apotential between electrode 1302 and ground plane 1304, ground plane1304 may be attracted towards electrode 1302 which, under specifiedconditions, may be capable of crushing aerogel 1303 into a benign powderas illustrated in FIG. 14. The crushing of aerogel 1303 may be able tocreate one or more voids. Since the constituent particles of aerogel1303 may be significantly smaller than the wavelength of light, thecrushing of aerogel 1303 may have no deleterious effect on pixel's 1300operation. Regions of aerogel 1303 which are not crushed may maintaintheir structural integrity since applied forces never exceeded theiryield strength in either shear or compression. Hence, the remaininguncrushed regions of aerogel 1303 may optionally serve as a resultingstandoff. Contiguous ground plane 1304 above the air gap generally has asuperadded elastomer or equivalent to provide restoring force forcontinuous mechanical actuation as illustrated in FIG. 15, and theelastomer may even be disposed on the surface of the contiguous groundplane 1304 facing aerogel 1303.

The present invention may be configured for systems of any lateralcomplexity so long as their cross-sectional dimensions fall within theproper range for electrically controlled compression of the sacrificiallayer to be pulverized. It is therefore extensible to a wide range ofMEMS applications. Further, it may be generalized to systems notspecifically using an aerogel, but any material capable of in situself-sacrifice under compressive strain applied according to anappropriate profile.

The generation of air gaps according to the present invention may notlikely to be a single step process, but rather may be likely to take amatter of minutes, hours, or longer, depending on the mechanicalproperties of the self-sacrificing layer. The process of ultimatelycrushing this layer generally proceeds exponentially, advancing fromapparent non-motion during the vast majority of the process to rapiddestruction of the sacrificial layer during the last 1-3% of theprocess, insofar as duration is concerned. The voltages required togenerate air gaps are likely to be far higher than for standard deviceoperation (operation after the airgap has been created). The signalprofile, frequency rate, and voltage may be determined by the mechanicaland electrical properties of the sacrificial layer. Square waves withextremely high slew rates provide the best results as opposed to othersignal profiles. Frequencies should be commensurate with clean squarewave generation, and should allow springback of the moving element,e.g., ground plane 1304, with any associated superimposed elastomerabove or below it to enhance net momentum transfer to the layer to becrushed, e.g. aerogel 1303.

It should be appreciated that traditional sacrificial layers may oftenbe removed using chemical etching compounds that invade the interior ofopen MEMS devices. These etching compounds may be targeted to attackonly the sacrificial layer and not the surrounding structures. Unimpededtransport of the compound to the sacrificial layer, and exhausting ofthe byproducts of the etching process away from the MEMS structure, arepresupposed. Where neither of these factors is present, the presentinvention may provide an alternate mechanism for achieving the sameresults for systems that lend themselves to its unique approach toregistration-free standoff and air gap construction. Although U.S. Pat.No. 5,319,491 may be a suitable candidate for implementation ofgenerating air gaps, the present invention is not limited to thatapplication.

The following is a list of criteria that may be required to generate airgaps and standoff structures without elaborate interlayer registration.It may be required for pixel 1300 to have intrinsic means to crush theself-sacrificing layer, e.g., aerogel 1303. Another criterion may bethat the force gradient during normal operation is such that thecrushing of the self-sacrificing layer is self-limiting, such that thelateral transition zone from void center to void perimeter (from crushedto semi-crushed to uncrushed standoff) will not exhibit mechanicalinstability that would lead to a loss of structural integrity. Further,the forces applied to the non-crushed regions may have to be configuredto fall under any such deleterious threshold. Alternately, contiguouspost-processing steps that enhance the mechanical integrity of thepost-generated air gaps and standoffs may be applied to secure this end,e.g., ultraviolet irradiation to further cure compounds amenable to suchprocessing. Alternatively, as a more complex variation, pre-processingthe self-sacrificing layer to make it anisotropic (weaker in the voidregions, stronger elsewhere) may be imposed, which would introduce thepotential necessity for registration and positioning means that may beotherwise obviated by the present invention. The pre-processing orpre-biasing of the self-sacrificing layer may be achieved by chemical,electrical, irradiative, thermal, or other means, alone or incombination, or achieved by exploitation of time-varying properties,whether global or local to the pixel vicinities, exhibited by the layerduring or after its fabrication. Further, the system in which air gapsand standoff structures are generated may be required no be immune toany ill effects from either the presence, or potential dispersion, ofthe residue arising from this process.

An illustration of generating air gaps and standoff structures beingapplied to an aerogel substrate one micron thick is illustrated in FIG.16. The fundamental principle is identical to that set forth in FIGS.13-15 except FIG. 16 illustrates actual components rather than line artidealizations. The choice of aerogel is, in this example, driven by itsultra-low refractive index, by which it serves as an ideal claddinglayer for a frustrated total internal reflection pixel mechanismutilizing the fourth embodiment of U.S. Pat. No. 5,319,491 that invokesevanescent coupling to emit light from the guidance substrate. It shouldbe appreciated that this enhancement is effectively a variation of thedevice shown in FIGS. 2A and 2B, corresponding to FIGS. 16 and 17,respectively, of U.S. Pat. No. 5,319,491, where elastomer layer 203 isreplaced with aerogel (which satisfies the optical requirements for thatlayer) which is subsequently crushed in the pixel vicinity to form anair gap (which still satisfies the optical requirements for that layer),allowing free excursion of the high refractive index region 205 into theevanescent field by plate bending motion peripherally supported by theuncrushed aerogel without continuously compressing layer 203, which hasbeen effectively self-sacrificed in the pixel vicinity under thisheading.

Although the method, circuits, mechanisms and apparatuses are descriedin connection with several embodiments, it is not intended to be limitedto the specific forms set forth herein; but on the contrary, it isintended to cover such alternatives, modifications and equivalents, ascan be reasonably included within the spirit and scope of the invention.It is noted that the headings are used only for organizational purposesand not meant to limit the scope of the description or claims.

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 15. A method forcreating an air gap between first and second layers separated by a thirdlayer comprising the steps of: applying an energy signal in order tocause the first and second layers to converge towards each other at apredetermined location resulting in a thinning of the third layer; andremoving the energy signal to thereby permit the first and second layersto rebound to a predetermined distance from each other, leaving an airgap at the predetermined location between the first layer and thethinned third layer.
 16. The method as recited in claim 15, wherein thefirst and second layers are parallel to each other.
 17. The method asrecited in claim 15, wherein the energy signal produces an electrostaticforce to converge the first and second layers towards each other. 18.The method as recited in claim 17, wherein the predetermined distance issmall enough to allow considerable mechanical force to be developedbetween the first and second layers by the electrostatic force.
 19. Themethod as recited in claim 17, wherein the electrostatic force exceeds amolecular bond strength of the third layer.
 20. The method as recited inclaim 15, wherein the third layer comprises an aerogel.
 21. The methodas recited in claim 15, wherein the third layer comprises a materialcapable of in situ self-sacrifice under compressive strain fromconvergence of the first and second layers.
 22. The method as recited inclaim 15, wherein the thinning of the third layer comprises a crushingof the third layer.
 23. The method as recited in claim 22, wherein thecrushing pulverizes the third layer.
 24. The method as recited in claim15, wherein the energy signal further comprises a high frequency squarewave electrical signal with high slew rates.
 25. The method as recitedin claim 15, wherein during the removing step the first layerelastically returns to the predetermined distance from the second layer.26. A method for creating a gap between layers at a pixel location in adisplay system, wherein the display system comprises a substrate, afirst conductor layer on the substrate, a second layer on the firstconductor layer, wherein the second layer comprises a material capableof in situ self-sacrifice under compressive strain, and a thirdconductor layer on the second layer, the method comprising the steps of:applying a high frequency electrical signal between the first and thirdconductor layers at the pixel location in order to cause the first andthird conductor layers to converge towards each other resulting in aprogressive compression of the second layer.
 27. The method as recitedin claim 26, further comprising the step of switching off the highfrequency electrical signal between the first and third conductor layersto thereby permit the first and third layers to rebound to apredetermined distance from each other, leaving a gap at the pixellocation between the first and second layers.